The proposed research is concerned with the total synthesis of naturally occurring alicyclic sesquiterpenes of a variety of structural types using photochemical methods. The plan of the approach to each compound generally can be divided into three parts: (1) the synthesis of an appropriate 6/6-fused or 6/5-fused cross-conjugated cyclohexadienone; (2) photochemical rearrangement of this compound to form the ring skeleton (or a precursor to it) of the target compound; and, (3) further modification of the photoproduct to produce the natural product itself. It is of major importance that the photolysis step generally proceeds with a high degree of stereospecificity and that products having many of the assymmetric centers of the natural product intact may be obtained directly. Total syntheses of the highly oxygenated tumor-inhibitory guaianolide (plus or minus)-euparotin, the cadinane sesquiterpene alcohols (plus or minus)-alpha-cadinol and (plus or minus)-T-murrolol, and the tricyclic hydrocarbon (plus or minus)-aromadendrene are in progress along these lines and their completion is proposed. A similar approach will be followed in proposed syntheses of the spirocyclic sesquiterpenes (plus or minus)-acorenone, B, and (plus or minus)-spirolaurenone, the hydroazulene (plus or minus)-mexicanin E, and the tricyclic compound (plus or minus)-zizanoic acid. In addition, methods of photochemical interconversion of sesquiterpenes of the nootkatane and vetispirane type via pathways involving cross-conjugated dienone and bicyclo(3.1.0)hex-2-en-3-one intermediates will be explored.